Abstract
Vascular relaxation action of crude extracts of two kinds of Coptidis rhizoma (Coptis chinensis andCoptis japonica, Ranunculaceae) was investigated and compared with that of berberine and palmatine, active alkaloid components of these plants. The results show that total extracts, berberine, and palmatine induced a concentration-dependent vasodilatation of rat thoracic aorta contracted with phenylephrine (PE). Palmatine, unlike to berberine, did not inhibit contraction induced by KCl. In calcium-free media, not only berberine but also crude extracts inhibited calcium-induced contraction. Furthermore, pretreatment of crude extracts inhibited contraction induced by PE noncompetitively. In PE-induced contraction, berberine was 2.5 times more potent thanCoptis chinensis in the relaxation of rat aorta in terms of IC50 values. Anlaysis of the effects of crude extracts on the Emax and IC50 (PE)/IC50 (KCl) ratios provides information on selectivity and indicates that extracts exhibit greater inhibition of the contrac tile response induced by PE than by KCl. We concluded that crude extracts have α-adrenoceptor blocking action and possesses inhibitory effect on calcium influx, which may be at least in part responsible for the antihypertensive action.
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